Search for: All records

Three-dimensional (3D) vision in augmented reality (AR) displays can enable highly immersive and realistic viewer experience, hence, attracts much attention. Most current approaches create 3D vision by projecting stereoscopic images to different eyes using two separate projection systems, which are inevitably bulky for wearable devices. Here, we propose a compact stereo waveguide AR display system using a single piece of thin flat glass integrated with a polarization-multiplexed metagrating in-coupler and two diffractive grating out-couplers. Incident light of opposite circular polarization states carrying stereoscopic images are first steered by the metagrating in-coupler to opposite propagation directions in the flat glass waveguide, subsequently extracted by the diffractive grating out-couplers, and finally received by different eyes, forming 3D stereo vision. Experimentally, we fabricated a display prototype and demonstrated independent projection of two polarization-multiplexed stereoscopic images. 

In this paper, a type of transparent colored static display consisting of a flat glass waveguide and embedded multi-layer gratings is presented, by which multiple patterns and colors with a wide field of view (FOV) can be displayed. The embedded grating is achieved by nanoimprinting followed by deposition of a high refractive index dielectric layer. The process can be repeated to produce multi-layer gratings, which are shaped into specific patterns to be displayed, and they are designed to have proper periods and orientations to independently extract light incident from different edges of the glass plate. Such transparent display offers the advantages of low cost, easy fabrication and wide FOV, and it is suitable for colored signage and decorative applications 

For those concerned with roll quality it is difficult to suppress the urge to compress the outer surface of a wound roll with your thumb to sense how tightly the roll was wound and how large the internal pressures might be. If several rolls of a given web are wound at unique tensions a human could often arrange these rolls in order of ascending winding tension using their thumb test. The thumb senses the relative conforming deformation of the roll surface. A soft roll would deform more and have greater contact area with our thumb than a hard roll for a given load. The thumb test is most useful on softer rolls wound from nonwovens, tissues, some grades of paper and polymer films but less so on metal coils that deform little in comparison to our thumb. The physics define stiffness as the extent to which an object resists deformation in response to an applied force. This publication reports the results of research where the stiffness of the outer surface of a wound roll is used to characterize the internal residual stresses throughout the roll due to winding. Measurements of stiffness of the outer surface of wound rolls will be demonstrated using commercially available devices along with a proposed handheld device all having greater resolution than the thumb. These measurements will be coupled with models to allow the exploration of internal residual stresses in the wound roll that can be used to investigate winding defects and roll quality. 

For convenience, webs are stored in wound rolls. The available web length in a wound roll is one mark of roll quality and a concern for many who process and convert webs. Elastic winding models have proven very precise at estimating the number of layers, the web length wound into a roll, and the residual stresses in the roll at the time of winding. Wound rolls can spend long periods of time in storage, where controlling the environment is cost-prohibitive. As many webs are viscoelastic on some time scale, the residual stresses due to winding will result in creep during storage. The changes in web length due to creep result in web process errors and quality loss, including registration errors and camber webs for example. This publication will focus on the development of a viscoelastic winding model to predict these changes in web length due to creep in a wound roll. The viscoelastic model predicts the tangential stress relaxation and radial creep due to winding residual stresses from a fully viscoelastic orthotropic material behavior. A spunned-meltblown-spunned (SMS) web and a low-density polyethylene (LDPE) web are taken as examples of viscoelastic webs. Their viscoelastic properties are systematically characterized using creep experiments. The results of the model show good agreement with winding and storage experiments for both webs. Finally, webs often do not creep uniformly across their width. An example of this non-uniform creep will be explored. 

While bending strains result from any web being wound at a radius of curvature into a roll, these bending strains are largest for the thicker homogeneous webs and laminates. Many webs are viscoelastic on some time scale and bending stresses will lead to creep. When the web material is unwound and cut into discrete samples, a residual curvature will remain. This curvature, called curl, is the inability for the web to lie flat at no tension. Curl is an undesirable web defect that causes loss of productivity in a subsequent web process. The goal of this research is to develop numerical and experimental tools by which process engineers can explore and mitigate machine direction curl in homogenous webs. Two numerical methods that allow the prediction of curl in a web are developed, a winding software based on bending recovery theory and the implementation of dynamic simulations of winding. One experimental method directly measures the curl online by taking advantage of the anticlastic bending resulting from the curl. All methods applied to a common isotropic LDPE web correlate well with each other and present an opportunity for process engineers to mitigate curl and its negative consequences at low time cost. 

The length of web in a wound roll is one mark of roll quality. The available web length in a roll is a concern for many who process webs and those who convert webs. There are algorithms that estimate the length of web and layers in a wound roll based on simple geometry and inputs of inside and outside radius and web thickness. If webs were infinitely stiff in the machine and out-of-plane directions such calculations could be accurate but this is not the case. Webs deform as the result of winder operating conditions such as winding tension and the contact pressures and stresses due to winding. Length calculations based on geometry will err as a result of web deformation in the length and radial directions. Webs are generally subject to tension during transport through process machines, the apparent deformed web length will vary with transport tension. The mission of this paper is to describe means by which the available deformed web length and the number of layers in a wound roll can be accurately predicted. The accuracy of the predictions will be verified by winding trials in the laboratory. The winding trials will demonstrate the levels of accuracy that can be realized on laboratory and production machines. 

The lateral deformations of webs in roll-to-roll (R2R) process machines can affect the quality of the manufacturing process. Webs can enter a cylindrical roller normally if the forces required to sustain normal entry and do not exceed the available friction forces. Webs with simple non-uniform length variation across their width (camber) will steer toward the long side, affecting the steady state lateral deformation and hence registration. Most previous studies have focused on tests and modeling a cambered web span in a free span between two rollers. Often these studies assume some displacement and slope boundary conditions are known and seek the remaining condition(s) that would dictate the steady state lateral deformation of the cambered web in the free span. In many spans in a process machine there may be no known boundary conditions and no steady state deformation of the cambered web. The web may travel toward the long side continually from one web span until the next until a web guide attempts to return the web to an acceptable lateral location in the process machine. The simplest case of multiple span cambered web lateral behavior is that of a cambered web belt transiting two aligned rollers which is the focus of the current work. Dynamic simulation (Abaqus/Standard) has been used to better understand the response of cambered webs under tension that has been witnessed in tests.